"Everything"? I just bought an iPaq machine and it uses Windows CE. Are you trying to sell me on something or are you telling the truth? :)
Depends on what you bought. If you bought one of the old CompaQ iPaqs it could very well have Windows CE OS on it.
Any of the current HP or Compaq iPaqs listed on the HP/Compaq site or in catalogs run the Pocket PC 2002 OS, as does the Toshiba's, Casio and ViewSonic.
Although I have not been a huge fan of Microsoft's attempts at palm sized computers (I prefer the Palm OS), I have been developing for handheld/palmtop systems since the Psion Series 3 in 1991.
The main problem in the past with Pocket PCs were too many different CPUs and having to compile your program for each CPU out there. With the exception of a few cheap Casio's everything seems to use the Intel ARM or the newer Intel X scale processors. The X scale can still run software compiled for the ARM. Less compatibility issues now.